There are several recent "for sale threads" listing limited amounts of rifle or handgun cartridges. I know this stuff can be shipped commercially but I have no idea what the requirements and/or restrictions include.

So what's the poop? If I were interested in sending small amounts of factory ammunition by USPS, UPS, or FEDEX what would it take to comply?

It's not cheap: shipping 15 shotgun shells halfway across country costs me about $12. Box size matters; part of charges based on total L + W + H of box. They try to brow beat you into using larger boxes "to deter theft" of a smaller, cheaper one.